The present invention generally relates to catheters. More specifically, the present invention relates to an improved catheter that may be used in mapping and ablation procedures of biological tissues.
For many years, catheters have had widespread application in the medical field. For example, mapping and ablation catheters have been extensively used in the treatment of cardiac arrhythmia. Cardiac arrhythmia treatments help restore the normal operation of the heart in pumping blood to the body. Mapping and ablation catheters play a critical role in these highly delicate treatments.
Typically, the catheters used in mapping and ablation procedures are steerable electrophysiological (xe2x80x9cEPxe2x80x9d) catheters that may be precisely positioned anywhere in the heart. These catheters are generally used during two distinct phases of treatment for heart arrhythmia. In one phase of treatment, the catheters are used to map the heart by locating damaged tissue cells. This involves the locating of damaged cells by steering the catheter to selected locations throughout the heart and detecting irregularities in the propagation of electrical wave impulses during contraction of the heart (a procedure commonly referred to as xe2x80x9cmappingxe2x80x9d). During the other phase of treatment, the same catheters are typically used to create scarring lesions at the location where damaged cells have been found (a procedure commonly referred to as xe2x80x9cablationxe2x80x9d).
Ablation procedures using EP catheters are typically performed using radio frequency (xe2x80x9cRFxe2x80x9d) energy. In this regard, an EP catheter has one or more ablation electrodes located at its distal end. The physician directs energy from the electrode through myocardial tissue either to an indifferent electrode, such as a large electrode placed on the chest of the patient (in a uni-polar electrode arrangement), or to an adjacent electrode (in a bipolar electrode arrangement) to ablate the tissue. Once a certain temperature has been attained, resistance heating of the tissue located adjacent the one or more electrodes occurs, producing lesions at the targeted tissue.
Referring to FIG. 1, a conventional catheter that may be used in mapping and ablation procedures is provided. FIG. 1 shows the distal end of a catheter. The catheter distal end comprises a body member 170, for example, a plastic tubing, and an electrode tip 160, attached to the distal end of the body member 170. A RF wire 150 runs through an irrigation channel 110, or alternatively through a separate lumen formed within the body member 170, and is connected to the electrode tip 160. At the distal end of the electrode tip 160 is a sensor 140, for example, a thermistor or a thermocouple, which is in thermal contact with the electrode tip 160. A sensor wire 145 extends from the sensor 140 back through the irrigation channel 110, or alternatively through a separate lumen formed within the body member 170. Ring electrodes 90 may be mounted around the body member 170. The electrode tip 160 is used to provide RF energy to heart tissues during ablation procedures. The RF wire connects the electrode tip 160 to a RF power supply (not shown). The ring electrodes 90 may be used together with the electrode tip 160 for mapping procedures.
Conventional catheters, such as those used for mapping and ablation procedures, are typically made entirely from a biologically compatible material, for example, a platinum iridium alloy (90 percent/10 percent). In general, however, the thermal conductivity of a platinum iridium alloy is not as high as that of other materials, such as copper or gold. One possible approach to increasing the thermal conductivity of an electrode is to form it from a material that is both biologically compatible and highly thermally conductive. However, many materials that are both biologically compatible and have highly thermal conductivity characteristics, such as gold, tend to be expensive.
As a result, catheter tips made entirely from economically feasible materials may be inefficient at dissipating excess thermal energy, thus creating thermal issues. Specifically, when excessive thermal energy is applied to a catheter electrode during ablation procedures, blood protein and other biological tissue may coagulate on the electrode, creating an embolic hazard. Such build up of coagulant on the electrode also hinders the transmission of RF energy from the electrode into the target tissue, thereby reducing the effectiveness of the ablation procedure. Ideally, it would be preferable to be able to focus the RF energy entirely on the targeted heart tissues without damaging the surrounding tissues or blood cells. That is, it would be highly preferable to be able to generate a good size lesion at a specifically defined area without altering, damaging, or destroying other surrounding tissue or blood.
In addition, it is generally desirable to be able to minimize the amount of time it takes to complete an ablation procedure. Typically, the longer it takes to complete an ablation procedure, the greater the health risk to the patient. Unfortunately, the time it takes to perform an ablation procedure may be related to how much thermal energy is directed towards the targeted tissue. That is, the greater the thermal energy directed towards the targeted tissue, the quicker the procedure can be performed. However, the amount of thermal energy that may be applied to the targeted tissue may be limited by damage that may potentially occur to the surrounding blood cells and tissues at highly thermal energy levels. For the above reasons, an EP catheter that is able to efficiently dissipate excess heat would be highly desirable.
The present inventions are directed to medical ablation electrodes that are capable of more efficiently dissipating heat during an ablation procedure.
In accordance with a first aspect of the present inventions, a medical ablation electrode comprises a biologically compatible outer layer, e.g., platinum iridium alloy, and a thermally conductive inner layer, e.g., copper. An irrigation channel is in contact with the inner layer for channeling cooling fluid. Preferably, the inner layer is in contact with the outer layer, e.g., by plating the outer layer onto the inner layer. In this manner, the conductive inner layer provides a highly conductive medium for increased heat dissipation from the electrode surface and its surrounding space, to an irrigating fluid flowing through the irrigation channel. The irrigating fluid then quickly removes the heat from the electrode during a heating operation, for example, during ablation.
In accordance with a second aspect of the present inventions, a medical ablation electrode comprises a thermally conductive proximal section having a substantially distally facing wall, and an irrigation channel formed within the proximal section for channeling cooling fluid. The electrode further comprises a thermally conductive distal section and one or more irrigation exit ports that extend through the distally facing wall of the proximal section. Thus, when cooling fluid is conveyed through the irrigation channel, it flows out through the exit ports over the exterior surface of the distal section, dissipating heat from the electrode.
In accordance with a third aspect of the present inventions, a medical ablation electrode comprises a thermally conductive housing having one or more concave sections and one or more convex sections, an irrigation channel formed within the housing for channeling cooling fluid, and one or more irrigation exit ports adjacent the one or more concave sections of the housing. In this manner, cooling regions are provided between the concave sections and the tissue to be ablated during the ablation process, whereby cooling fluid conveyed out of the exit ports from the irrigation channel enters the cooling areas to cool the tissue.
In accordance with a fourth aspect of the present inventions, a medical ablation electrode comprises a spiral-shaped thermally conductive irrigation tube having an irrigation channel. In this manner, the area of the irrigation channel exposed to the cooling fluid is maximized. In this case, the housing may form a single unitary structure that can be composed essentially of a biologically compatible material, which otherwise may not be feasible absent the additional cooling of the electrode.
In accordance with a fifth aspect of the present inventions, a medical ablation electrode comprises a thermally conductive rigid housing and one or more flow-through channels formed by an external surface of the rigid housing for channeling biological fluids over the external surface. As a result, the external surface of the rigid housing is increased by use of the flow-through channels.
In accordance with a sixth aspect of the present inventions, a medical ablation electrode comprises an inner cylinder having an inner irrigation channel extending therethrough for channeling cooling fluid. The electrode further comprises an outer cap that is mounted in a concentrically overlapping arrangement with the inner cylinder, such that an annular irrigation channel is formed between an inner surface of the outer cap and an outer surface of the inner cylinder for channeling the cooling fluid. In this manner, the cooling fluid flows over the inner and outer surfaces of the inner cylinder, thereby maximizing thermal dissipation of the heat into the cooling fluid. In a preferred embodiment, the inner cylinder and outer cap are composed of a thermally conductive biologically compatible material, and are mounted to each other using a pin. The electrode can further include one or more irrigation exit ports that are in fluid communication with the annular irrigation channel.
In accordance with a seventh aspect of the present inventions, a medical ablation electrode comprises a thermally conductive housing, and an irrigation channel formed in the housing for channeling cooling fluid. The housing in thin-walled, i.e., the wall of the housing has a thickness that is less than the diameter of the irrigation channel divided by the number 2. In this manner, the heat transfer rate through the housing wall in increased, thereby increasing the amount of thermal energy dissipated into the cooling fluid.
Thus, as can be seen, that in accordance with the second through seventh aspects of the present inventions, the electrode structure can be composed essentially of a biologically compatible material, which otherwise may not be feasible absent the additional cooling of the electrode and/or tissue. Alternatively, however, the housing can be composed of a highly thermally conductive inner layer and biologically compatible outer layer, or can be composed purely of a highly thermally conductive, but biologically compatible material, such as gold, to further increase the cooling of the electrode.